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Two photon reconstruction with ECAL and low mass background Alexei Stavinskiy, Konstantin Mikhaylov ITEP, Russia. A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 1. Input.
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Two photon reconstruction with ECAL and low mass background Alexei Stavinskiy, Konstantin Mikhaylov ITEP, Russia A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 1
Input 2*104 central UrQMD events AuAu@25AGeV (Local analysis) Full ECAL reconstruction (version of February 2009) with CBM root January 2009 version (version with new geometry) Cuts: Minimal energy deposited in ECAL 500 MeV. χ2 (of photon reconstruction) < 3. Minimal distance between cluster (DBC) > 20 cm. Particles from target = Vz < 1cm (conventional) A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 2
WA 98 experiment [arXiv:nucl-ex/0006007] A low mass tail on the π0 was observed. The tail can result from π0 produced downstream from target: • from decays (K0s, ...) • from background interaction on downstream materials (the normalized target out background contribution is shown by the open circles In part c)) A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 3
1t 1b θb θt 2b πtarget πbackground 2t • Differences between target and background pairs: • *mean photon energy higher for target photons *real emission angle difference for target photons from π(η) decay corresponds to measured invariant mass; this is not the case for background pairs • *vertex position is fixed for target pairs; • for background pairs vertex position distribution • corresponds to detectors (support) position A.Stavinskiy K.Mikhailov ITEP CBM collaboration meeting, March 2009 4
Mγγsame mother A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 6
Mγγ vs Vz π0 ECAL RPC TRD3 TRD2 TRD1 RICH A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 7
π0 mothers vs Vz For 0 with Vz>1. mothers: code % production -321 1.9% K- ->pi-pi0 cτ=3.7m -211 22.1% pi- 130 2.2% KL0 ->pipipi0 cτ=15.34m 211 14.5% pi+ 310 22.2% Ks0 ->pi0pi0 cτ=2.7m 321 4.5% K+ ->pi+pi0 cτ=3.7m 2112 11.9% n 2212 10.9% p 3122 5.6% Lambda->npi0 cτ=7.8cm 3222 3.6% Sigma+ ->ppi0 cτ=2.4cm 3322 0.4% Xi0->Lambdapi0 cτ=8.7cm Vz PDG code A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 8
Pi0 mothers vs Vz K- π- π+ KL0 K+ n p Σ+ Ξ0 KS0 Λ A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 9
XYECAL for different VZ Materials X0 A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 10
Ecut: π0 Z-vertex vs Mγγ A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 11
Ecut Rcut: Mγγ,same mother S/B for 0<Mγγ<200MeV A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 12
Ecut Rcut: Mγγ,same mother S/B for 0<Mγγ<120MeV A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 13
DBC cut: Mγγ,same mother Distance Between Clusters>20cm Distance Between Clusters>50cm A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 14
DBC > 50 cm, Ecut Rcut S/B for 0<Mγγ<120MeV A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 15
Signal and Background K.Mikhaylov ITEP CBM collaboration meeting, March 2009 16
Signal-Background VZ<1cm S/sqrt(S+B)=20 S/B=0.25% K.Mikhaylov ITEP CBM collaboration meeting, March 2009 17
Correlation function (S/B) K.Mikhaylov ITEP CBM collaboration meeting, March 2009 18
Correlation function (S/B) VZ<1cm K.Mikhaylov ITEP CBM collaboration meeting, March 2009 19
A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 20
Two-photon correlations e+ 2 2rec 1 1 e- • External conversion: • No close cluster interference • No hadron contamination C2 calculated in EMCAL and converted+EMCAL agree => both effects are under control A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 21
Measurement of Direct Photons via Conversion in CBM Melanie Klein-Bosing WWU Munster,Germany CBM Collaboration Meeting, Dubna 2008, October
Conclusions • The feasibility of π and η meson identification with ECAL was shown • The low mass background in two photon invariant mass was studied • Two main contribution to the low mass background are: • Interaction with downstream detector construction • Decay of long lived particles • Possible cuts to reduce (slightly) low mass background: • Cut on gamma energy • Cut on distance between center of clusters • Other possible ways: • Background simulations • Combined photon pair identification with different detectors
1t e1b 2t πtarget e2b Possible source of low mass background A.Stavinskiy K.Mikhailov ITEP CBM collaboration meeting, March 2009 25
R-dependence A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 26